Image amplifier phototimer



Sept. 23, 1958 B. DE WITT' IMAGE AMPLIFIER PHOTOTIMER Filed Aug. 16. 1951 INVENTOR Benjamin DeWih. ATTORNEY WITNESSES: 5477 1 technique; and; made fluoroscopic examinations. much v asses-19* MAG BHQ O'HMER: 5

Benjamin De Witt, Baltimore,. Md:, assignor-to' W'stinge hou se-;E-l'ectric; Corporation; EastPittsburgh, Pa., a corporationof 'Pennsylvania yr uve tiq e e ates totimi s .d eeand. nart cur, lar;- comprises-arr arrangement/for.- timing; the; operation, ofi; a source r of X-rays or; otherpenetrating 3- radiation; in accordancevwith the amounttof suchradiation which has-. penetrated ant-object,being-irradiated, It is applied withi particular. advantage to X-ray. apparatus; which. enr-.. bodies an X-ray image intensifier such .as that showmand. describe c1 in Mason. and; Coltrnan. U. S'.;. Patent No. 15 35 5325 It; islbecomingta more andmore desirable-practice inia making X-ray, examinations: particularly-in; the, medical field, to employ fluoroscopy that is, to viewtheimageof. the,object-being-irradiated;on a fluorescent:screen'. While itqh as been the practicetonmany years;to;follow"this: practice; glfQfitydlfl'iCllllYf has always I beenexperienced: from; the dimness; of the fluorescent: image,v which; has: beenso; great -.th;at the observerhas had :to: wait in; adark. ened roormdor periods'iofi the-order of-. thirtv-w'or-.forty.- minutesto adapt histeyes to the'low-light levelghe must- WOIk; With. Thev above. mentioned patent: describes. arr imageqintensifier having .a. fluorescent screen; vat its .input endrandrhaving an electron-phosphor screen at itsoutput end on whichv an imageofabrightness something overone hundredtimes that on thefluorescentscreen is produced. This arrangement has practically revolutionized, X-.ray

more :useful than, theyhave ever been before'.

- The great-intensification. of brightness achieved in -this imageintensifier is brought about by positioning a photoelectric screcnclose-to the fluorescent screen, thereby produe ing an electron image which duplicates'in. spacedis-. tributionthe lightimage-producedby the X-r ays;on v the. fluorescent, screen, and accelerating I thiselectron image into incidence on v the electron phosphor output screen; On the latter. there is; thus produced a light image of; greatly" intensified brightness, whichv may; be viewed, through a suitable light-optical system, or maybe photo: graphedr either still ormotion, for permanent record,

' As, isswell known.,the .durationz and intensity of gthe X-raybeam are limited toundesirably low values in rnedical .work bythe harmful effects of too great exposure of: the patient to the rays. The use of other types ofpenetr-ating radiation than X-rays, for example, beams .ofneutronsQis also,slowlycoming ,into practice, nd is ,subject to similar limitations due to exposure danger. It is .accordingly necessary to provide for terminating the irradiating beam after a predetermined amount of exposure to to the radiation. This can be done automatically in the case of apparatus employing imageintensifiers since'the number of electrons which has been emitted from the. photo-electric screen is directly proportional to the numher of roentgensofX-rays to which the patient has been exposed atlanytime.

Onev object of my invention .is accordingly to provide animprovedsXqay apparatusin which a; great increasei's attainedjn the brightnessof a-fluorescent image while at thetsarne time thedosage of, X-rays to which the pa.-. tient is exposed is terminated at a desired value.

ice

Another object ;,ofmy,1inven ion:is' tosprovideianzimproved image, intensifier apparatuspwhich; automatically; intensifies the;brightness: of' f the image 1on v a; fluorescent screen and; at the; same time controls theyag rh'sy. -producev nsthe mage; H'-i CQI:dfi 1 Q:Wifl1; hei ime-integ ch intensity.

Another object is; to -.p r;ovidet an arrangementin which visible pictures. are; generatedq by; penetrating; radiationz and imwhich the sourcegof -radiation is ,CQHtIOllGdwlILfiOl'f respondence; ith thettime interval of-theradiation which:

f has:at nvn ns a tt. e e:ateclthevpict rer.

Still another object oflmy nventiongiseto provide: an rrangemeetahi h isibl -tim ess. produced :by pence a n a v a o are=photograph d:-a d: p sr p ing;;apparatus is controlled-tin accordance with theetotal amount ;-of; radiation which has been employed.

'fiet anothenobject of, lmyginvention isto ,providetantape paratus -producing visibl pictures through 1116; employ? t f penetrating;radiation,;which automatically ini-z and -jtCIII1iI1 ,QS.E h-Q: flowt1of radiationt from. its source; in correspondence with; the total; amoun.t:of;;radiatiom which has been employed-in th sPiQfl116=,=

A further; .objecti-is,- to.pro videwan :X-r-ay apparatus-. for flDQmsGopy;,in-;Which;- an-;-,image intensifier ramplifiesrther brightness; of the.-.image on; the, fluorescent screen, with; means; for 1 photography recording the image in Whiclu meansh :zph o raphi rp surevis. automatically 'r s lated to EICCOIdwWiih; theqbrightness of thegpictureibeingt pho gr phed.

Other} objects ot'i my; invention; will'gbecomev apparent from; reading;- the following 5 description takerr1in-;,connec-; tio with: the drawing; in the single figure; is. agsche-z matte;representationtofi an X-ray system embodyinghant image intensifier; and; equipped; with controls in accord-z ance; with;the-princip1es-pf1my invention.

Referring indetail:to.-the -drawing;,a sourcesof pene-: trating radiation such as am x rayttubel of any; suitable type. is positioned to; transmit-ta beam of radiation-throughany-desired :object'xonto the; inputscreen :of .an image ;in;-. tensi-fier- Zj'tWhlCh is shown here for; illustrative pnnposes as .ofqthe generaltypedescribed2 ;in ;the -abo.ve mentioned: Mason; and Coltmanpatent; Thisimage intensifier! 2. comprises an input soreemih'aving a layer:offluorescent: materialrsuch asr zincvsulphide separatedybyr thirnglass from a screen of ph-oto-electrically emissive material such. as "cesiatedantimony. At the-oppositeend -of-the-tube -21 is positioned :an output "screen -.4- ihaving-:a1=thin layer; oftam electron-phosphor,whichemayvbe .szinc cadmium -sulphidee The illbfigziis highly evacuated and; mayt betprovidedin the space between screens 3 and 4 Witha suitable-relocatronzlens 1 system described in .more; detailgin the above mentioned :patent... A t suitable voltage 'source: 9; havingt itsnegative; terminal :groundedeimpresscs 1a high: positive voltage. on; thetscreen 4. 7

As described in the above; mentioned patent {radiations transmitted. from the source ,:1 through; the :o-bjectbeing; examined strikes the, fluorescent ,-'screen;3,- thereby=produc-= ing a; r light-image. which; generates on the, photo-electric. screen immediately contiguous. to it, an -electron. imagecorresponding-with it point. by.point;over-the,- area of the screen. The positive output screen 4-- accelerates; the: electrons composing thisimage which arezfoeused by thfii electronlens-system to produce,.,uponzirnpact with;the-.- electron phosphor layer a light-(image, which ;is :a replica; to very much reduced dimensions, of .thelight, image on; the. screen 3 If itis desired; 'thiS.1igh lE,j image on screen t4 'zmay;-,- be; view dr h u a l i h ropt a ys e uret r-: ably. a. magnifying one, whereby ,aHIigh-Limage substan tially like. that on the inppt screen, 3 exceptthat .its brightness..has.,been; greatly.magnifiedv may: be seen .by, an, observer. However for certain purposes it' is frequently desired to make a photographic record of the light image on the screen 4 and this may be done by suitably operating a camera 5 which is preferably provided with an electrically controlled shutter 6.

When the radiation source 1 is energized a flow of electrons will be initiated from the photo-electric surface on the input surface 3 to the output screen 4, thereby setting up a current flowing to ground through the voltage source connected to screen 4 and thence back to the input screen 3 through a resistor 7 and lead 8.

The X-ray source 1 is energized by a transformer 11 having a primary winding connected through the normally open contacts of a relay 12 to a suitable source 13 of alternating current voltage. The energizing winding of the relay 12 may be connected to the voltage source 13 through the normally closed contacts of a relay 14 and a hand switch 15. The energizing winding of relay 14 is connected in the main electrode circuits of a gas discharge tube 16 which is provided with a control electrode. The relay 14 and the tube 16 are shunted across a resistor 17 which is fed from the positive terminal of the direct current voltage source 18 through the normally open contact of a relay 19. The negative terminal of the voltage source 18 is grounded. The energizing winding of the relay 19 is connected through the hand switch 15 across the terminals of the voltage source 13.

The end of the resistor 17 which is remote from the normally open contact of the relay 19 is connected through a resistor 21 to the anode of a grid-controlled electron tube 22 which is here shown as a tetrode and also through a pair of resistors 23 and 24 to ground. The anode of the tetrode 22 is connected through a variable resistor 25 to the control electrode of the tube 16. The control grid of the tube 22 is connected to the ungrounded end of the resistor 7. A capacitor 26 is shunted between the control grid and the cathode of the tube 16, and is shunted by a pair of normally closed contacts on the relay 19. When it is desired to employ the automatic shutter 6 on the camera 5 it may be connected in shunt across the input terminals of the transformer 11.

The mode of operation of the above described system is as follows: When the hand switch 15 is closed current flows through it and the normally closed contacts of relay 14 to energize the relay 12 from the power source 13. Relay 12 energizes transformer 11 thereby .causing a beam of X-rays from the source 1 to irradiate the input screen 3 of the image intensifier tube 2 after transmission through the object under observation. The light image thus generated on the screen 3 produces a corresponding electron image, the electrons of which flow through the tube 2 and the resistor 7 thereby producing a positive voltage on the control electrode of the tube 22, and at the same time producing a light image on the output screen 4.

It will be noted that the normally closed contacts of the relay 19 maintain a short circuit across the capacitor 26 until relay 19 is energized. When the hand switch 15 was closed as above described it energized the relay 19 to open this short circuit about the capacitor 26 and at the same time to close its normally open contacts thereby connecting the lower end of the resistor 17 to the positive terminal of the voltage source 18. As a result of the closure of these normally open contacts a positive potential is impressed on the anode of the tetrode 22 and current flows through the latter tube by way of the resistor 21 and its shunt path including resistor 25 and the capacitor 26 to the positive terminal of the source 18 by way of the resistor 17. The flow of this current through the capacitor 26 starts to build up a charge on it but it has sufficient capacity so that the control grid of the tube 16 is not immediately effective to start current flow between the main electrodes of the latter. Closure of the normally open contacts of the relay 19 also connected the upper electrode of the tube 16 through the energizing winding of the relay 14 across the potential drop due to current in the resistor 17. Since the control electrode of the tube 16 was initially at the potential of its lower electrode that tube was non-conducting and no current flowed through the energizing winding of the relay 14. However, sufiicient voltage soon builds up on the capacitor 26 to initiate an arc discharge through the tube 16 whereupon the relay 14 is energized to open its closed contacts and thus interrupt current flow through the energizing winding of the relay 12. The contacts of the latter then open to interrupt current flow from the source 13 to the X-ray tube 1 and to the shutter mechanism 6. Thus the X-ray beam from the tubel is cut ofi after a time fixed by the interval required by the capacitor 26 to charge up to a voltage sufiicient to initiate current flow through the tube 16. The length of this interval can be set at any desired figure by adjusting the variable resistor 25.

The voltage drop through the resistor 7 is proportional to the intensity of the X-ray beam striking the fluorescent screen of the image intensifier 2; and it is this voltage drop thr ugh the resistor7 which determines the rate of current flow through tetrode 22 to charge the capacitor 26. The more intense the X-ray beam from source 1, the greater the current flow through tetrode 22 and the more rapidly will the capacitor 26 charge sufliciently to initiate current flow through tube 16 thereby interrupting further flow of the X-ray beam. Thus the beam is interrupted when the time integral of its intensity reaches apredetermined figure, the latter being variable at will by adjusting the variable resistor 25.

Since the automatic shutter 6 is connected across the circuit supplying the transformer 11 it will be evident that this shutter is opened when that transformer initiates the X-ray beam and is shut When the X-ray beam is itnerrupted. Thus the time integral of the light exposure f the film behind shutter 6 is likewise fixed at a predetermined value by the charging of the capacitor 26. While the contacts of relay 12 are shown as connected in series with both the transformer 11 and the shutter 6 it is believed to be obvious that they may be connected in either one of these circuits alone if control of the corresponding apparatus in accordance with the X-ray dosage should be desired.

After termination of the X-ray exposure by opening of the contacts of relay 14, the relay 12 cannot be reenergized until the switch 15 has been opened. The opening of that switch deenergizes the energizing winding of relay 19 thereby opening its normally-open contacts to cut 011 current flow through resistors 17, 23 and 24, from the D. C. source 18. The gaseous discharge tube 16 is thus extinguished upon the cessation of current flow through resistor 17, permitting the normally closed contacts of relay 14 to close so that the energizing winding f relay 12 may be energized when manual switch 15 is next closed. At the same time that relay 19 is thus deenergized its normally closed contacts are shut and quickly dissipate the charge of capacitor 26. The system has thus been returned to the initial condition in which it stood at the time the foregoing operation cycle commenced.

While I have described my invention as used to administer a predetermined dosage of X-rays it will be evident that it may be employed to control in accordance with a predetermined time integral of radiation any type of apparatus for which such a regulation is desirable.

I claim as my invention:

1. In combination with a source of X-rays, an image intensifier including a photoelectric member to produce an electron spaceimage of an object irradiated by said source and an electron responsive fluorescent member spaced from said photoelectric member to generate a visible light image in response to impingement of said electron space-image, and means for controlling said source of X-rays including an electric circuit connected to one of said members so as to be traversed by the electrons constituting said electron space-image.

2. In a fluoroscopic apparatus having a source of X-rays for producing an X-ray image of an object irradiated by said source, an image intensifier including a fluorescent screen responsive to said X-ray image, a photoelectric screen member positioned adjacent said fluorescent screen to produce a space distributed electron image having the pattern of said X-ray image, and an electron-phosphor screen member spaced from said photoelectric screen member for receiving said electron image to produce an intensified visible light image, and an electric circuit connected to one of said members for controlling said source to limit the duration of said X-ray image, said electric circuit including first circuit means traversed by electrons forming said image and second circuit means connected between said first circuit means and said source to control said source in response to the passage of a predetermined number of electrons through said first circuit means.

3. In combination with a fluoroscopic apparatus including a source of penetrating radiation, an image intensifier including a photoelectric member to produce an electron space-image of an object irradiated by said source and an electron-phosphor member spaced from said photoelectric member to produce a visible image in response to impingement of said electron space image thereon, and an electric circuit for controlling said source including circuit means connected to one of said members and traversed by electrons forming part of said spaceimage.

4. In combination With a fluoroscopic apparatus including a source of penetrating radiation to produce a radiation image of an object, an image intensifier including a photoelectric member to produce an electron image having the pattern of said radiation image and an electron phosphor member spaced from said photoelectric member to produce a visible light image in response to impingement of said electron image, photographic apparatus for recording said light image, and an electric circuit including circuit means connected to one of said members and traversed by electrons constituting said electron image with said electric circuit being connected to said photographic apparatus to interrupt the operation thereof in response to the passage of a predetermined number of electrons through said circuit means.

5. Apparatus for making photographs comprising an image amplifier for converting an X-ray image into a light image including'a photo-cathode and an anode, a source of potential coupled to said cathode and anode, a camera including film optically coupled to said image amplifier for photographing said light image produced thereby, and means coupled to said source and responsive to the current flow between said cathode and anode for controlling the correct exposure of said film.

6. Apparatus for making photographs comprising an image amplifier including a photo-cathode and an anode for converting an X-ray image into a light image, a source of potential coupled to said cathode and anode, a camera including film optically coupled to said image amplifier for photographing the light image produced thereby, and means coupled to said source and responsive to the current flow between said cathode and anode for controlling the correct exposure of said film, said means including a capacitor arranged to be charged by said anode cathode current, and means responsive to the voltage across said capacitor to terminate the X-ray image to thereby stop further exposure of the film.

References Cited in the file of this patent UNITED STATES PATENTS 2,305,452 Kallmann Dec. 15,1942 2,401,289 Morgan et a1 May 28, 1946 2,441,324 Morgan et a1 May 11, 1948 2,523,132 Mason et a1 Sept. 19, 1950 2,535,817 Skellett Dec. 26, 1950 2,555,545 Hunter et al. June 5, 1951 2,586,392 Sheldon Feb. 19, 1952 2,595,430 Tuttle May 6, 1952 2,561,085 Zavales July 17, 1952 2,622,219 Schagen Dec. 16, 1952 2,790,085 Fransen et a1. Apr. 23, 1957 

